Radial-flow fans of this kind take in air, another gas such as methane or an air-gas mixture from a working environment and convey it whilst both the flow rate as well as the pressure of the medium transported rises.
The primary intent of this type of fan is to improve the fan power performance characteristic and to adapt it to the desired application. There is also a great need for radial fans that at the specific fan power performance characteristic that is as high as possible at the same time produce little noise since these types of radial fans are frequently used in places in which noise is perceived as unpleasant. Various measures have been proposed in the state-of-the-art to improve the performance characteristic and at the same time reduce the noise levels of fans. For example there are radial fans known in which between the tab of the casing and the fan wheel a wedge-type gap is provided for this purpose at the tab which considerably reduces running noise.
Different tab shapes are known which are also designed to reduce running noise, the so-called turning sound that occurs in particular when the blades of the fan wheel rotate past the tab.
A radial fan is known from German Patent DE 100 17 808 A1 that has inlet vanes in the compression space to direct the air flow in the compression space to the exhaust. This allows for a higher specific fan power. This in turn also reduces noise development. With regard to other necessary increases in efficiency and ever stricter requirements in the area of noise development, this arrangement, however, is also in need of improvement.